One cause of the increased referral rate for in-vitro fertilization is the growing prevalence of overweight and obesity. Currently, about 700 couples are annually referred for in-vitro fertilization at St.Olav's Hospital. In this interdisciplinary trial, involving physiotherapists, exercise physiologists, gynecologists, and basic researchers, the effects of regular high intensity exercise training on fertility in sub-fertile overweight and obese women will be investigated.